Erm...you don't seem to understand the very nature of a butler.
Of course Aya's cooking shouldn't make sense. However, being a representation of order, Alvarez tries all he can to make sense to what he sees.
The reason why I was half-tempted to call the melted cabbage soup wasabi is because cabbage would adopt a similar color, and because Alvarez isn't well trained with Japanese cuisine. However, DJ went with the "green jelly", which wouldn't make sense as wasabi is a paste, not a jelly. The closest thing to that would be konyaku jelly, deliberately colored as cabbage would.
After all, if the master were to ask, he has to give an explanation, right?